It sounds like you already have an idea of some of the best things to do in Oregon (skiing!), and you really can’t go wrong with either option, but I can offer some more details that might help you decide.
March tends to be the best month for skiing in the Cascades! We usually get quite a bit of snow in February and March. You’ll want to make sure to factor this into your travel plans and be prepared for snow conditions if you drive to Sisters or even up to Mt. Hood via Hwy 26. Bend is about three hours from the Portland area in good conditions, but it is a gorgeous drive over the mountains. Sisters, Bend, and Sunriver are all great options in terms of small towns with shops, good restaurants and breweries, though Bend and Sisters have a little bit more to offer simply due to their larger size. Bend and Sunriver are closer to Mt. Bachelor, which is convenient especially if the weather is inclement. I love exploring the little shops in both Bend and Sisters and I would be happy to recommend places to eat or drink if you’re interested.
If you opt for Mt. Hood, you certainly won’t have to drive as far and it would be easy to ski one day and check out the Columbia River Gorge for another day or two. Sandy and Government Camp are cute small towns, and Government Camp has some yummy food options and also the feeling of being in a real mountain town. For small shops to check out, I’d suggest Hood River. It’s a great town at the base of Mt. Hood and right on the Columbia River. There are plenty of quaint shops, cafés, breweries and restaurants, and there’s a nice path for walking along the river. It’s also close to both Mt. Hood Meadows Ski Area and many of the best Columbia River Gorge hiking trails.
If I were you, with three days to spend after flying into PDX, I would probably head for Hood River and ski Mt. Hood Meadows, then check out Hood River and the Columbia River Gorge. I think you could do the most from there. However, like I said, you really can’t go wrong with either option!